80sc sputters/no power after it warms up.
 

Hello,
Took the car an a long road trip this weekend (4hrs) for the first time since I rebuilt my engine 6mo ago. The car has run fine since the rebuild on trips of a 2hrs or less. About 2 1/2 into my trip I notice a loss of power. By the time I made it to my parents house it was sputtering and backfiring slightly. I looked it over, suspecting a vacuum leak or a hose or wire came loose. I took it out for another drive after it cooled for a few hrs and it ran fine then after about 20 min it started to sputter again??? I left the car at my parents and took my 68 vett home....which is another challenge :) anyway, I plan on returning to my parents this weekend and do the followings checks: Coil...I have another one sitting around so ill switch it out, replace the fuel filter, preform the fuel pressure check on the CIS (i'll post the results) Change out the spark plugs since their cheep. Check the distributor, cap and rotor for cracks, and check the timing. Also, the fuel pump is new but is a cheep one...might be heating up and not working properly. I replace almost everything new when I did my rebuild. I did not replace the WUR however. Have I overlooked anything I should check? Has anyone had a similar experience? I did alot of searching and found similar threads but no success stories?

Thank you!
Alan

What CDI box do you have? Many posters have mentioned that their Permatunes of a certain vintage tend to lose power once heated up. Also, let us know what your fuel pressures are.

My Permatunes would just die while running then the car would start up again. Never had a sputtering issue. Just D E D dead for 20 mins up to a couple hours.

Your O2 relay may be acting up. Under the passenger set.

Make sure your frequency valve is working when the car is acting up. It will vibrate. If it's not working then that may be your problem. Face the engine and find the air bypass screw. The freq valve is three inches away - down at a 45 degree angle. Like a fat injector. There is a recent thread where there was a bad connection in the big connector on the back wall of the engine compartment causing the freq valve to fail when outside temps were really high.

Hello, Thank you for the replies, The CD box is stock original. Also, I don't have an o2 sensor...so do I have a frequency valve...that narrow it down a little. I'll check the frequency valve and do a search on it. I'll post the CIS pressure #'S another mystery :) Thank you again for the replies!

Alan

I forgot to ask. I have been mildly flamed before for yakking about the O2 system to folks with ROW cars. Sorry about that.

Folks talk about looking up Early_S_Man posts for good info. Maybe you could filter on Bosch CD and use his name as the filter?

If you hook up the gauges I would run (drive) the car with the gauges on until the symptoms start.

You did not mention plug wires in your list. Check for arcing in the dark and/or check the resistance on the wires - Of course - if they are bad when hot they will read good when you check them. :-)

Hello! Thank for the info :) The plug wires are new as is most of everything else...that's why I'm kinda stumped. I did forget to mention that before when I removed the oil cap at idle it ran rough now it doesn't make much of a difference. I have however, increase the CIS to run a little richer since. If it doesn't run rough with the oil cap removed this usually, indicates a vacuum leak?? Those are hard to find :( I'll figure it out eventually...I hope!
Thanks!
Alan

I found three vacuum leaks after my "no way could I screw something up" refresh of the miscellaneous engine seals. My RPMs do drop on my 81 with the oil cap removed and I believe yours should too being an 80. There was a thread a month or two ago about earlier 911s not having the same oil breather piping the 2.7s and 3.0s had and the RPMs do not drop. I think the change-over was post 75.

Get some starting fluid and take the chance of engulfing your face in a ball of fire and spray it on the vacuum connections while running. RPMs will change.

Check the gold cadmium plated space ship disc connections (AAV and Decel) on the passenger side as well as the AAR between 5 & 6 intake runners. The AAR has a tapered snoot and if the connection is loose the hose may have slid off.

Check your injectors for proper seating and the brass tube that hooks into the throttle body and ties in your brake vacuum booster. My brass tube can actually pull out of the throttle body by hand if both mounting points are not affixed. The tie in to the brake hose is a "V" off the back of the brass tube (well - the plastic part of it) around the 2/3 cylinder runners and is hard to see.

Hi! Thanks again for the responses. I'll do all the above this weekend. Since the car is 4hrs away I'm at a disadvantage....I'm still searching posts and will continue till I get it figured out. I have a lot of good info to go on :) Frustrating, not having the car in my garage....It was quite a trip...the clutch pedal broke in half...this happened in traffic...that was a major WTF!!! Anyway, Thanks again!!

Alan

Alan,
What year is your car?

I had an '80 SC CIS and my Bosch box did the same thing. The warmer it got, the worse it ran.

Couldn't find a reasonable Bosch and put in a Permatune, ran fine for years.

Hi Tcar,
I have an 80sc euro. No o2 sensor. Hummm....how did you come to the conclusion that the stock bosch box was bad? Thanks for the info. greatly appreciated :)
Alan

i am not sure if your year still had points but i use to have a 71 240 that when the points got pitted or the gap closed out it would do that.

Hello, Thanks for the reply kanadary. It doesn't have points. I'm going to tackle the CIS pressure tests this weekend and go from there....Hoping it will shed light on what is going on :)
Thanks again!
Alan

Beyond my diagnostic skills... took it to Storz Garage here in Denver, they figured it out.

Might want to snag an MSD 6AL and a Blaster coil before taking the trip. Cost will pinch but if you don't need it you can take it back. You can do a "sloppy" install to get it home then tidy things up at your own place. To do it right it takes a weekend (with breaks) for the semi-experienced DIY mechanic. Follow the instructions and make sure it is really well grounded - e.g., Not the aluminum plate by the fuel filter.

CIS troubleshooting..........
 

Alan,

The fact that you changed the air-fuel mixture setting richer to improve the idle is a sign of lean mixture due to unmetered air. If your warm idle RPM does not drop significantly (example:from 950 down to 650-750), you have unmetered air!!!! Do a pressure test by pressurizing the system with compressed air.

Many people having problem locating the source of the vacuum leak say they couldn't find one. Not being able to locate the source of the vacuum leak/s does mean you don't have one!!!! So stop guessing and do the test.

But before you go chasing the problem, make sure that you have good ignition timing, ignition sparks, fuel pressures (control & system), acceptable CO level (measured by a gas analyzer), and no significant vacuum leak that could affect the fuel to air mixture. Keep us posted.

Tony

Hello thanks for the replies!
Yes, Tony your correct....I did the cold pressure test this weekend....it was 4.8 bar. I can't do the worm pressure tests till I get he clutch pedal replaced. It broke in half...I ordered another one but will be a week or two bf I can get it installed and drive the car. I did start it and let it run for 15 or 20 min and it ran fine. But, the problems begins with the engine fully warmed up and a load placed on it. I also pulled all the spark plugs and cranked the engine with the plugs connected. All have spark...it was dark out so they lit up well. I really appreciate the replies...you all are a great help! I do suspect I have an air leak somewhere. I didn't have time to check that this weekend. It might be thanksgiving bf I make it this way again.....

4.8 bar is your system pressure not the cold control pressure.

Hello,
I think I got it fixed. I replaced the CD box with another used one. It seemes to run fine now. Thank for all the help! :)
Alan